Polymeric biomaterials are used in every diagnostic or therapeutic device or implant in the cardiovascular system. Nevertheless, when flowing blood is contacted with most if not all of such biomaterials, varying degrees of thrombosis and thromboembolism result. These events represent major deterrents to the development and application of new or improved heart assist devices and cardiovascular implants, especially for longer term uses. In this Program Project, our objectives are to develop a fundamental understanding of the cause and effect relationships between the biomaterial bulk and surface character and its propensity to cause thrombosis or thromboembolism and then to endothelialize (especially for fabric prostheses) when contacted in vivo under different, well defined hemodynamic situations with flowing blood. We propose to do this by synthesizing new or modified polymeric biomaterials, characterizing their surface chemical composition and physical topography, measuring their interactions with blood and its components in vitro, and then in vivo in an A-V shunt test system on baboons.